This study seeks to examine by quantitative immunocytochemistry the regulation of the quantity of the catecholamine biosynthetic enzyme tryosine hydroxylase (TH) within individual neurons of central noradrenergic and dopaminergic neurons of the rat CNS in response to treatment with the psychoactive drugs, reserpine, and the central muscurinic agonist oxotremorine. It will attempt to: (a) validate a technique for quantitative immunocytochemistry of TH in brain utilizing a feature-specific image analysis system in conjunction with the preoxidase-antiperoxidase technique; (b) determine the relative amount of TH enzyme within individual neurons of the noradrenergic locus ceruleus (LC) and dopaminergic substantia nigra (SN) and their projection fields: (c) determine if there is a variation in the amount of TH protein between neurons within specific nuclear groups (e.g., LC or SN) and by analysis of total amount of enzyme protein per neuron; with respect to its topography in the nucleus (d) determine whether the increase in amount of TH produced by treatment with reserpine is topographically selective and to contrast it with the effects of activation of TH produced by oxotremorine; and (g) to ascertain whether cold stress increases TH accumulation in selective populations of LC neurons and compare the changes in amount and distribution with changes in the enzyme elicited by reserpine.